1. Field of the Invention
The present invention relates to a photographic film cassette. More particularly, the present invention relates to a photographic film cassette containing an entire length of a photographic filmstrip therein so as to be capable of advancing out of the cassette shell in response to an unwinding rotation of a spool about which the photographic filmstrip is coiled. More specifically, the present invention relates to a photographic film cassette having a spool lock mechanism for preventing rotation of the spool and a light-shielding door for closing a film passage mouth to shield ambient light from entering the cassette interior.
2. Background Art
For example, U.S. Pat. Nos. 5,296,887, 5,317,355 and 5,319,407 disclose photographic film cassettes, in each of which a photographic filmstrip is entirely contained in a cassette shell, and when a spool is rotated, the leader is responsively advanced to the outside of the cassette shell. These patents also disclose a light-shielding door that is adapted to be rotated by a specific drive shaft of a camera so as to open the film passage mouth, and a spool lock mechanism interconnecting between the spool and the light-shielding door so as to prevent rotation of the spool when the light-shielding door is closed.
The spool lock mechanism as disclosed in U.S. Pat. No. 5,317,355 is shown in FIGS. 10A, 10B and 10C. A locking member 200 is a single-piece device comprising first and second resilient arms 201 and 202 and a support extension 200a supporting the second arm 201. The support extension 200a and the first arm 201 converge to a common base 203. The locking member 200 is supported for pivotal movement at the base 203 about an axis pin 204. The axis pin 204 is formed on an inner surface of a cassette shell 205 of a photographic film cassette 206. A film passage mouth 209 of the cassette shell 205 is provided with a light-shielding door 210.
FIG. 10A shows a closed position of the light-shielding door 210, wherein a free end 201a of the first arm 201 is in contact with a cam 211 of the light-shielding door 210 and a protuberance 212 on the support extension 200a is in engagement with a gear portion 216 of a spool core 215, such that the locking member 200 is deformed under a compressive force. Due to the resiliency of the first arm 201, the light-shielding door 210 is secured closed. Also the protuberance 212 is pressed against the gear portion 216, so the spool 215 is secured to be not-rotatable. The secure arm 202 has a click 202a at its free end. The click 202a interlocks with a protrusion 219 formed on the inner surface of the cassette shell 205.
After the photographic film cassette 206 is loaded in a camera, the light-shielding door 210 is rotated by a drive shaft of the camera into an open position as shown in FIG. 10B, wherein the free end 201a of the first arm 201 is disengaged from the cam 211, so the locking member 200 recovers its original shape. As a result, the urging force of the locking member 200 toward the spool core 215 is so diminished that the spool core 215 is made rotatable. Thereafter when the spool core 215 is rotated in an unwinding direction as shown by an arrow in FIG. 10C, a tooth of the gear 216 pushes the protuberance 212 on the support extension 200a, thereby bending the support extension 200a toward the light-shielding door 210. As a result, the click 202a passes over the protrusion 219 to fix the locking member 200 in its unlock position shown in FIG. 10C, wherein the protuberance 212 is disengaged from the gear 216, so the spool core 215 is kept rotatable. Further rotation of the spool core 215 in the unwinding direction causes a not-shown photographic filmstrip to advance out of the cassette shell 205 through the film passage mouth 209.
FIGS. 11A, 11B and 11C show the spool lock mechanism as disclosed in U.S. Pat. No. 5,319,407, wherein a locking member 250 is a single-piece yoke-shaped device. The locking member 250 is pivotal about a pivot protuberance 251 which protrudes outwards to be supported in a socket 253 formed on an inner surface of a cassette shell 252. A free end 256 of the locking member 250 is engaged in a recessed surface 259a of a cam 259 formed with a light-shielding door 255. A locking tooth 261 is formed in a middle portion of the locking member 250 to protrude inwards therefrom.
When the light-shielding door 255 is closed as shown in FIG. 11A, the locking tooth 261 is engaged with a gear 263 of a spool core 262 to prevent rotation of the spool core 262. The spool core 262 can be forcibly rotated in the unwinding direction as shown by an arrow in FIG. 11B. When the spool core 262 rotates, a tooth of the gear 263 pushes the locking tooth 261 outwards, so that the locking member 250 is forced to rotate about the pivot protuberance 251 in a direction to remove from the gear 263. As a result, the free end 256 pushes a protrusion 259b of the cam 259 to rotate the cam 259 in a direction to open the light-shielding door 255. When the light-shielding door 255 is set in the open position as shown in FIG. 11C, the free end 256 of the locking member 250 is supported by another protrusion 259c of the cam 259 so as to keep the locking tooth 261 away from the gear 263.